1. Field of the Invention
This invention relates to a door scope, and more particularly to an improvement in a door scope which is an optical device provided in a door for viewing outside from inside of the door.
2. Description of the Prior Art
It has been known in the art to provide an optical device in a door for viewing outside from inside. (This optical device will hereinafter be referred to as a "door scope"). The conventional door scope consists of an objective of large diameter, an eyepiece, and a pair of auxiliary objectives provided immediately behind the objective. The pair of auxiliary objectives are both planoconcave and the concave faces of the objectives are faced to each other. In a door scope, the angle of view is desired to be as large as possible. Further, the conventional door scope has a defect in that the optical system has a chromatic aberration since all the lenses are made of the same glass material.
Further, the conventional door scope has a defect in that it is possible to peep therethrough from outside.